The present invention relates to a sealed thrust bearing which is used in a vehicle, particulary, which is assembled into a strut forming a suspension for supporting front wheels of the vehicle.
In a suspension of a strut type that supports the front wheels of a vehicle serving as the steering wheels thereof, a damper case forming an oil damper is supported in such a manner that it can be moved up and down with respect to the body of a vehicle. The front wheels are rotatably supported on a pivot fixed to the lower end portion of the damper case, while the oil damper is supported such that it can be freely rotated with respect to the vehicle body. Therefore, between the upper end portion of a rod forming the oil damper and the vehicle body, it is necessary to dispose a thrust bearing which supports the rod rotatably while receiving a thrust load.
As a thrust bearing to be used in such portion, conventionally, there is known a sealed thrust bearing which is disclosed in, for example, U.S. Pat. No. 4,780,005. As shown in FIG. 7, the sealed thrust bearing includes an outer race 1 and an inner race 2 respectively formed in an annular shape, and a plurality of rolling elements 3 respectively held between the outer race 1 and inner race 2. In the conventional thrust bearing shown in FIG. 7, the rolling elements 3 are with balls. In the case of a thrust bearing is used in a bulky vehicle, other rolling elements can be used such as a tapered roller and the like.
The outer race 1 includes an outer raceway 4 on one surface thereof (a lower surface viewed in FIG. 7) and an outer flange 5 in the outer peripheral edge thereof. Also, the inner race 2 includes an inner raceway 6 on one surface thereof (an upper surface viewed in FIG. 7) and an inner flange 7 in the inner peripheral edge thereof. Further, the plurality of rolling elements 3 are rollably interposed between the outer raceway 4 and inner raceway 6 and permit the rotation of the outer and inner races 1 and 2 relative to each other.
Moreover, an outer seal ring 8 is interposed between the outer flange 5 and the outer peripheral edge of the inner race 2, while an inner seal ring 9 is interposed between the inner flange 7 and the interior portion of the thrust bearing locating near the inner periphery of the outer race 1. These seal rings 8 and 9 include core metals 10a, 10b and elastic elements 11a, 11b, respectively. The core metal 10a forming the outer seal ring 8 is fitted into and fixed to the outer flange 5, while the end edge of a lip 12a of the elastic element 11a reinforced by the core metal 10a slidingly contacts the outer peripheral edge of the inner race 2. Also, the elastic element 11b forming the inner seal ring 9 and reinforced by the core metal 10b is fitted over the inner flange 7, while the end edge of a lip 12b formed in the elastic element 11b slidingly contacts the portion of the outer race 1 locating near the inner periphery of the one surface (lower surface viewed in FIG. 7) of the outer race 1.
As described above, the interposition of the two outer and inner seal rings 8 and 9 between the outer and inner races 1 and 2 not only can prevent outward leakage of grease existing in the portion where the plurality of rolling elements 3 are held but also can prevent foreign matter such as dust, rain and the like from entering into such portion. Also, the engagement between the lip 12a of the outer seal ring 8 and the outer peripheral edge of the inner race 2 can prevent the inner race 2 and outer race 1 from being separated from each other even before the sealed thrust bearing is assembled into a predetermined position. This makes it possible to handle the respective components of the sealed thrust bearing in an integral manner, so that the assembling operation of the sealed thrust bearing can be simplified.
Also, Unexamined Japanese Utility Model Publication No. Hei. 5-79047 has proposed such a structure as shown in FIG. 8. In the structure shown in FIG. 8, not only the lip 12a of the outer seal ring 8 is engaged with the outer peripheral edge of the inner race 2, but also the lip 12b of the inner seal ring 9 is engaged with the inner peripheral edge of the outer race 1. As a result of this, when compared with the structure shown in FIG. 7, it is capable of obtaining a higher separation preventive effect between the outer and inner races 1 and 2.
However, in both of the conventional sealed thrust bearings structured in the above-mentioned manner, there are still found some problems to be solved. That is, in either of the above two structures, the lip 12a of the elastic element 11a of the outer seal ring 8 supported by the outer flange 5 is exposed externally. Also, in the structure shown in FIG. 8, not only the outer lip 12a but also the inner lip 12b are exposed externally.
During use of the vehicle, rain or mud tends to splash on the sliding portions between the externally exposed end edges of the lips 12a, 12b and their respective mating surfaces (that is, the inner peripheral edge surface of the inner race 2 and the inner peripheral edge surface of the outer race 1). Also, after the splashed mud dries, foreign matter such as the mud, dust and the like are left on the sliding portions, so that there is a possibility that such foreign matters may act as an abrasive to damage the end edges of the lips 12a, 12b and their mating surfaces. As a result of this, the end edges of the lips 12a, 12b and their respective mating surfaces may wear quickly to thereby lose the ability to prevent the rain and mud from entering into the rolling elements provision portion.
The above-mentioned wear can be further increased due to rust produced on the mating surfaces. In most cases, the outer and inner races 1 and 2 to be incorporated into the sealed thrust bearing for use in the suspension system are wholly formed of carbon steel, and surface treatment layers such as an electro-zincing layer or the like are formed on the surface of the outer and inner races in order to protect them against corrosion. However, if such wear increases greatly due to the foreign matter in the sliding portions, then the surface treatment layers are worn away to expose the carbon steel, with the result that the exposed carbon steel portion gathers rust. And, the rust scrapes the end edges of the lips 12a, 12b to thereby accelerate further the wear of the end edges.